Back seam welder and method of operation

ABSTRACT

A thermal welder is configured to weld a back seam of a bag formed of thermoplastic sheet material. The welder may include a weld heater and a compression mechanism downstream of the weld heater to compress the sheet material to form the back seam. The welder may also include a weld breaker downstream of the compression mechanism to break apart incidental welds which are formed adjacent the back seam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/253,325, filed Apr. 15, 2014, which application claims priority fromU.S. Provisional Application Ser. No. 61/811,997, filed Apr. 15, 2013;the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Technical Field

The invention relates generally to a bag production machine andfabrication process. More particularly, the invention relates to athermal welder for welding thermoplastic sheet material. Specifically,the invention relates to a thermal back seam welder and method which maybe used to form polywoven bags.

Background Information

A great many types of bags are formed and manufactured along aproduction line. To properly store a material or liquid in such bags,seams created during the bag formation process must be properly sealed.Some machines form seams using adhesive, hot melt glue, stitching orsome other material that is distinct and separate from the material thatforms the panels of the bag itself. However, sealing or seaming machineshave not been configured to weld or seal the back seam of a bag usingonly heat and compression to weld the back seam. Stated otherwise,sealing machines have not been configured to weld the back seam of a bagwithout using adhesive, hot melt glue, stitching or some other materialthat is distinct and separate from the bag material. The presentinvention addresses this and other issues.

SUMMARY

In one aspect, a thermal welding apparatus may comprise a sheet materialpathway adapted to allow sheet material to move downstream therethrough;a weld heater extending adjacent the pathway; a compression mechanismextending adjacent the pathway adjacent and downstream of the weldheater; and a weld breaker assembly which comprises a first axial legupstream of the compression mechanism, a second axial leg downstream ofthe compression mechanism, and a longitudinal leg extending from thefirst axial leg to the second axial leg; wherein the second axial legserves as a weld breaker which is within the pathway and adapted todisengage incidental welds created during formation of a welded backseam of the sheet material as the sheet material is moving downstreamthrough the pathway.

In another aspect, a combination may comprise flexible thermoplasticsheet material in a tubular configuration comprising first and secondsuperimposed panels, wherein the second panel includes a first segmentand a second segment overlapping the first segment along an overlapregion; a thermal welding apparatus through which the sheet material ismovable downstream; a weld heater of the thermal welding apparatusextending adjacent the overlap region; a compression mechanism of thethermal welding apparatus which is adjacent and downstream of the weldheater and which compresses the first and second segments and the firstpanel; a welded back seam formed between the first and second segmentsdownstream of the compression mechanism; incidental welds formed betweenthe welded back seam and the first panel; and a weld breaker assemblywhich comprises a first axial leg upstream of the compression mechanismand a second axial leg downstream of the compression mechanism, whereinthe first axial leg extends between the first and second segments, thesecond axial leg extends between the welded back seam and the firstpanel, and the second axial leg serves as a weld breaker whichdisengages the incidental welds as the sheet material moves downstream.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more sample embodiments of the invention, illustrative of thebest mode in which Applicant contemplates applying the principles, areset forth in the following description and are shown in the drawings andare particularly and distinctly pointed out and set forth in theappended claims.

FIG. 1 is a diagrammatic side view of a bag manufacturing productionline.

FIG. 2 is a top plan view of a sample embodiment the thermal back seamwelder of the present invention taken along line 2-2 in FIG. 1.

FIG. 3 is a side elevation view taken along line 3-3 in FIG. 2.

FIG. 4 is a an enlarged top plan view taken along line 4-4 in FIG. 3showing a portion of the preheating manifold, the shield plates, theweld heater, the weld rollers, and the weld breaker.

FIG. 5 is an enlarged section view taken along line 5-5 in FIG. 4.

FIG. 6 is an enlarged section view taken along line 6-6 in FIG. 4.

FIG. 7 is a top plan view similar to FIG. 2 showing sheet materialmoving downstream.

FIG. 8 is an enlarged cross section taken along line 8-8 in FIG. 7showing the upstream drive roller, the upstream idle roller, aseparation shaft, an upstream preheater manifold and the sheet material.

FIG. 9 is an enlarged cross section taken along line 9-9 in FIG. 7looking downstream.

FIG. 10 is an enlarged cross section taken along line 10-10 in FIG. 7looking downstream.

FIG. 11 is similar to FIG. 4 and shows the sheet material movingdownstream past the preheating assembly, heater shield assembly, weldheater, weld rollers, and weld breaker.

FIG. 12 is a side cross section view similar to FIG. 6 taken along line12-12 in FIG. 11.

FIG. 12A is a side cross section view taken along line 12A-12A in FIG.11.

FIG. 13 is a cross section view looking downstream taken along line13-13 in FIG. 11.

FIG. 14 is a cross section view facing downstream taken along line 14-14in FIG. 11.

Similar numbers refer to similar parts throughout the drawings.

DETAILED DESCRIPTION

With primary reference to FIG. 1, a thermal welding apparatus or welder10 is configured to weld a back seam 11A (FIG. 7) formed of flexiblesheet material 11 which typically unrolls from a material roll 12 andmoves in a downstream direction or flow stream (Arrows F) from upstreamcomponents 14 to downstream components 16 of a production line 18.Material 11 moves within a sheet material pathway 9 (FIGS. 2-14) havingleft and right sides 9C and 9D (FIG. 7) defining therebetween a width 9A(FIGS. 2, 7) and top and bottom boundaries 9E and 9F (FIGS. 8-10, 12-14)defining therebetween a thickness 9B (FIG. 8) which varies as material11 moves in the downstream direction. Components 14 typically include abag former or tuber configured to form sheet material into a tubularconfiguration which moves downstream through welder 10. Components 16typically include a bottomer configured to form a seam along the bottomedge of the bag after back seam 11A has been formed. Back seam 11A isdescribed in the U.S. patent application Ser. No. 14/253,387 titled “BAGWITH THERMAL WELDED BACK SEAM” which was filed on Apr. 15, 2014,published as US Patent Application Publication 2014/0307987, and isincorporated herein by reference as if fully rewritten herein. Flexiblesheet material 11 is a thermoplastic material capable of being thermallywelded to itself and typically strong enough to store a volume of bulkmaterial when formed into a bag. Material 11 may be polypropylenealthough other thermoplastic materials may be used as well. Sheetmaterial 11 may be a polywoven material.

Referring primarily to FIGS. 2 and 3, thermal welding apparatus 10 hasan upstream end 3 and a downstream end 4 defining therebetween alongitudinal direction, a left side 5 and a right side 6 definingtherebetween an axial direction, a top 7 and a bottom 8. Welder 10includes a rigid frame 2 extending from adjacent left side 5 to adjacentright side 6 and from adjacent upstream end 3 to adjacent downstream end4, an upstream drive roller 20 adjacent upstream end 3, an upstream idleroller 22 adjacent upstream end 3 and roller 20, a downstream driveroller 21 adjacent downstream end 4, a downstream idle roller 23adjacent downstream end 4 and roller 21, a rigid first sheet materialseparating shaft 24, a preheater assembly 26, a rigid second sheetmaterial separating shaft 28, a heat or heater shield assembly 29 havinga first or upper shield plate 30 and a second or lower shield plate 32(FIG. 5) spaced apart and below first shield plate 30 wherein first andsecond shield plates 30 and 32 define therebetween a heater passage 34(FIG. 5), a weld heater 36 a portion of which extends within passage 34,a compression mechanism 38 located closely adjacent and downstream ofweld heater 36, and a rigid weld breaker assembly 39 comprising a rigidweld breaker 40 positioned downstream of the compression mechanism 38.

With primary reference to FIGS. 2 and 8, upstream drive roller 20 ispositioned upstream of weld heater 36 and extends axially and generallyorthogonally across or perpendicular to downstream direction or flowstream F of bag material 11. Upstream drive roller 20 is generallycannular in shape and has an axial length 44 greater than axial width9A. Upstream drive roller 20 has a cylindrical outer surface 46 definingan outer diameter 42 (FIG. 2) of roller 20, which may be constructed ofmaterials as one would understand in the art which are used to contact aflowing sheet of formed bag material. The top of outer surface 46 ofupstream drive roller 20 defines a portion of lower boundary 9F of sheetmaterial pathway 9. Roller 20 is rotationally secured by bearing 48 toframe 2. A drive mechanism 50 is operatively connected to roller 20 andmay be a motor as conventionally known in the art configured to driverotation of roller 20 about an axis X1 (FIG. 3) which is typically anaxially extending axis which in the sample embodiment is substantiallyhorizontal.

Upstream idle roller 22 is closely adjacent roller 20 and may bedirectly above roller 20. Roller 22 has a cylindrical outer surface 54which defines an outer diameter 52 (FIG. 2) of roller 22 which issmaller than that of upstream drive roller 20. The bottom of outersurface 54 of idle roller 22 defines a portion of upper boundary 9E ofsheet material pathway 9. The portions of outer surfaces 54 of roller 22and 46 of roller 20 which are closest to one another are closelyadjacent one another and define therebetween a portion of passage 56(FIG. 8) of pathway 9. Idle roller 22 is rotationally connected 48 toframe 2, permitting roller 22 to rotate about axially extending axis X2,which is parallel to axis X1. Directly between axes X1 and X2, outersurfaces 46 and 54 may be in contact with or closely adjacent oneanother and may be spaced apart a distance approximately similar to thethickness of flowing sheet material 11. When moving downstream (ArrowsF), material 11 passes through flow passage 56. Drive roller outersurface 54 and idle roller outer surface 46 contact material 11 asmaterial 11 flows downstream through flow passage 56. While bag material11 is flowing downstream, drive roller 20 rotates (Arrow R1 in FIG. 8)about axis X1 in the opposite direction of the rotation (Arrow R2 inFIG. 8) of idle drive roller 22. For example, when upstream drive roller20 rotates in a clockwise manner, idle drive roller 22 rotates in acounter-clockwise manner. This permits material 11 to continuously flowF through flow passage 56.

Separating shaft 24 (FIGS. 2, 8) is adjacent and downstream of upstreamrollers 20 and 22. Shaft 24 may be in the form or an axially elongatedrod and may have a cylindrical outer surface defining an outer diameterof shaft 24 which may be in a range of about one-half or one inch tothree or four inches in diameter, although other dimensions arecontemplated. Shaft 24 has first and second (left and right) opposedends 24A, 24B which are axially spaced from one another. Shaft 24 has asegment 24C including end 24A that is outside of sheet material pathway9 and a segment 24D including end 24B that is inside sheet materialpathway 9. Segment 24C extends axially from adjacent first end 24A tosegment 24D, which extends from segment 24C to end 24B. Shaft 24 isrigidly secured at first end 24A in a cantilever fashion to frame 2 andextends axially to free or terminal second end 24B. First separatingshaft 24 typically extends from adjacent left side 5 across andtypically perpendicular to flow stream F partially across width 9A ofsheet material pathway 9 so that internal segment 24D including terminalfree end 24D is entirely within pathway 9. Shaft 24 is typicallystraight and horizontal from adjacent end 24A to adjacent end 24B.

With primary reference to FIGS. 2 and 3, preheater assembly 26 isadjacent and downstream of separation shaft 24. Preheater assembly 26comprises a first or upstream manifold 60, a second or downstreammanifold 62, a heat source (e.g., an electric heater), a blower and anaxial adjusting carriage 64. A portion of heater assembly 26 extendswithin sheet material pathway 9. More particularly, each of manifolds 60and 62 is within pathway 9. Manifolds 60, 62 are longitudinallyelongated and typically are straight and horizontal from adjacent anrespective upstream end 59 to adjacent a respective downstream end 61 ofthe given manifold. Upstream end 59 of manifold 60 and assembly 26 isadjacent and downstream of upstream rollers 20 and 22, and downstreamend 61 of manifold 60 is distal and downstream of upstream rollers 20and 22 and the upstream end 59 of manifold 60. The upstream end 59 ofmanifold 62 is adjacent and downstream of the downstream end 61 ofmanifold 60, and the downstream end 61 of manifold 62 and assembly 26 isdistal the upstream end 59 of manifold 62 and adjacent and upstream ofdownstream separation shaft 28. Manifolds 60 and 62 are substantiallyparallel to one another and the flow stream direction F. Manifold 62 istypically directly downstream of manifold 60 such that the two manifoldsare substantially collinear.

Each of manifolds 60 and 62 may have sidewalls 65 which define aninterior chamber 63 extending from adjacent the upstream end to adjacentthe downstream end of the respective manifold. Each manifold 60 and 62may have formed in the sidewalls 65 thereof a plurality of apertures orholes which serve as air outlets 66 which extend from the respectiveinterior chamber 63 to the outer surface of the respective sidewall 65and thus to atmosphere external to the given manifold. Preheaterassembly 26 further comprises a heater and a blower operativelyconnected to each other and in communication with the interior chamberof manifolds 60 and 62 whereby when the heater and blower are turnedon/powered, the heater heats air which the blower blows to moved heatedair into the interior chambers 63 of the manifolds and out of theirrespective air outlets 66. Preheater assembly 26 is axially adjustablevia adjusting carriage 64 along directional arrow 27 (FIG. 2) toaccommodate polywoven or other sheet material 11 of various sizes. Thus,preheater assembly 26 can be positioned axially at any desired locationso that manifolds 60 and 62 are within any desired portion of pathway 9to preheat longitudinally elongated portions of sheet material 11 usedto form back seam 11A (FIGS. 11, 12).

With primary reference to FIGS. 2 and 4-6, second separation shaft 28 isadjacent and downstream of the downstream end 61 of manifold 62 andpreheater assembly 26. Shaft 28 has first and second (left and right)opposed ends 28A and 28B which are axially spaced from one another suchthat shaft 28 is axially elongated therebetween. Downstream shaft 28 maybe substantially straight and horizontal and parallel to upstream shaft26. Shaft 28 is typically in the form of a rod which may have acylindrical outer surface defining an outer diameter of shaft 28 ofabout ½ inch although other dimensions are contemplated. Shaft 28 has atop 68 and a bottom 70 each of which is on the cylindrical outer surfaceof shaft 28 where shaft 28 is configured in cylindrical form. Shaft 28is rigidly secured at first end 28A in a cantilever fashion to frame 2and extends axially to free or terminal second end 28B. Shaft 28 is thussecured along and extends from one side 5 of frame 2 toward the otherside 6. Shafts 26 and 28 are thus secured along the same side of frame 2and extend axially toward the opposite side. Shaft 28 extends part waybut not all the way across the width of pathway 9. Shaft 28 extendsacross flow stream F typically perpendicular thereto and is partiallywithin pathway 9. More particularly, shaft 28 has a segment 28Cincluding end 28A that is outside of pathway 9 and a segment 28Dincluding terminal end 28B that is inside pathway 9. Segment 28C extendsaxially from adjacent first end 28A to segment 28D, which extends fromsegment 28C to end 28B.

With primary reference to FIGS. 4-6, heat shield or heater shieldassembly 29 includes a plate assembly 31 and shaft 28. Plate assembly 31includes first and second shield plates 30 and 32. First plates 30 isentirely within sheet material pathway 9. A portion of plate 32 is inpathway 9 and a portion of plate 32 is outside of pathway 9. A portionof segment 28D of shaft 28 directly upstream of plates 30 and 32 may becalled a heat shield segment of shaft 28, such that a combination of theheat shield segment and plates 30 and 32 defines heater passage 34 inwhich a heating tip or welding tip of heater 36 is received. Plateassembly 31 may also include a plate or lip 84 which is substantiallyparallel to and directly above plate 30. Plate 30 and lip 84 aretypically formed of a single piece of sheet metal which also includes aconnecting wall or bend 85 which extends between and is rigidly securedto plate 30 and lip 84. Bend 85 is longitudinally elongated and extendsupwardly from plate 30 a short distance so that lip 84 is adjacent andspaced upwardly of plate 30.

Plate 30 has an upwardly facing flat outer or top surface 72 and adownwardly facing flat inner or bottom surface 74 each of which extendsfrom a first (left) longitudinally elongated side edge 71 to a second(right) longitudinally elongated side edge 73 of plate 30. Surfaces 72and 74 also extend from an axially elongated upstream end or edge 75 toan axially elongated downstream end or edge 77 of plate 30. Bend 85extends upwardly from side edge 71 to the left side edge of lip 84. Lip84 has a downwardly facing flat bottom surface 79 which is adjacent andspaced upwardly of top surface 72 of plate 30 so that bottom surface 79and top surface 72 define therebetween a sheet-edge receiving space orguide passage 81 having an upstream entrance opening, a downstream exitopening and a (right) side entrance opening. Passage 81 is closed on itsleft side by connecting wall or bend 85. Passage 81 is a small portionof pathway 9. In the sample embodiment, lip 84 extends axially only partof the way across plate 30 although this may vary. The upper portion(plates 30 and 84 and bend 85) of plate assembly 31 are secured to frame2 by a rigid plate mounting leg or rod 83 which may extend upwardly fromthe upper portion of assembly 31 perpendicular to flat plates 30 and 84.A first or upper end of rod 83 is rigidly secured to frame 2 and extendsdownwardly therefrom in a cantilever fashion to a second or bottomopposed free or terminal end which is rigidly secured to the upwardlyfacing top surface of plate 84. In the sample embodiment, the rigidconnection between plate 84 and the bottom of rod 83 is the onlyconnection between the upper portion of plate assembly 31 and the restof welder 10, such that said upper portion is suspended at the bottomend of rod 83 and out of contact with any other portion of welder 10.

Plate 30 is generally adjacent and downstream of segment 28D of shaft 28and generally adjacent and upstream of a pair of pinch rollers ofcompression mechanism 38. Upstream end 75 is adjacent and downstream ofsegment 28D and at about the same height as top 68 of shaft segment 28D.Downstream end 77 is adjacent and upstream of the pinch rollers ofcompression mechanism 38. Plate 30 extends downstream from adjacentsegment 28D toward compression mechanism 38 and may angle downwardlyrelative to horizontal and towards lower plate 32 in the downstreamdirection so that downstream end or edge 77 may be a little lower thanupstream end or edge 75.

With continued primary reference to FIGS. 4-6, lower plate 32 extendsdirectly below upper or intermediate plate 30 and top plate 84. Plate 32has a downwardly facing flat outer or bottom surface 76 and an upwardlyfacing flat inner or top surface 78 which faces, is adjacent and isspaced downwardly from bottom surface 74 of plate 30. The welding tip ofheater 36 is between plates 30 and 32 and adjacent inner surfaces 74 and78. Plate 32 has first (left) and second (right) longitudinallyelongated opposed side edges 82 and 80. Plate 32 has an axiallyelongated upstream end or edge 87 and an axially elongated downstreamend or edge 93. Plate 32 is rigidly secured along upstream edge 87 toshaft 28 adjacent bottom 70 and extends downstream therefrom incantilever fashion to free or terminal downstream edge 93. Downstreamend 93 is adjacent and upstream of the pinch rollers of compressionmechanism 38. End or edge 93 is adjacent and spaced directly belowdownstream edge 77 of upper plate 30 so that edges 93 and 77 definetherebetween a downstream exit opening 91 of heater passage 34.

Plate 32 extends downstream from adjacent bottom 70 of rod 28 towardcompression mechanism 38 and may angle slightly upwardly relative tohorizontal and towards first plate 30. Thus, the upstream end (adjacentedge 75 of plate 30) of passage 34 may be vertically wider than thedownstream end of passage 34 adjacent edges 77 and 93. Passage 34 maythus narrow in the downstream direction. Plates 30, 32 and 84 aretypically formed of a sheet metal or another material which may becapable of withstanding temperatures at least 1450° F. or more whilemaintaining the structural integrity of the plates and/or withoutmelting.

Weld heater 36 includes a heat source (e.g. an electric heater) and ablower in fluid communication with the heat source and an air source.Weld heater 36 may be axially adjustable as show by arrow 37 in FIG. 2.Heater 36 has an air tube 89 defining a hot air passage which extendsalong the entire length of tube 89, an upper inlet end 90 defining anair inlet, and a lower front outlet end 92 having a nozzle 94 definingan air outlet 96. The air inlet of inlet end 90 is in fluidcommunication with the blower of heater 36 so that blower 36 when turnedon blows heated air (heated by the heat source of heater 36) through thehot air passage of tube 89 from the inlet end 90 to the outlet end 92and out of exit opening 96. Tube 89 includes a first or upwardlyextending or vertical leg 95, a second or axial leg 97 which is securedto the bottom end of leg 95 and extends axially therefrom (to the right)to a distal (right) end distal the bottom of leg 95, and a third orlongitudinal leg 99 which is secured to the distal end of leg 97 andextends longitudinally downstream to a downstream end which defines exitopening 96. Leg 99 serves as a welding tip of heater 36 which includesexit opening 96 and is within heater passage 34 with exit opening 96upstream of, adjacent and facing downstream toward exit opening 93 ofpassage 34. Exit opening is thus in fluid communication with heaterpassage 34.

Exit opening 96 of nozzle 94 and exit opening 93 of passage 34 permitshot air 86 (Arrows 86 in FIG. 12) to exit nozzle 94 and passage 34 intospace immediately downstream of exit opening 34 and upstream of thepinch rollers of compression mechanism 38. Exit opening 96 has an axialwidth typically in a range of about one-half or one inch to about threeor four inches although this may vary. An axial width of about one inchis suitable in many cases. Exit opening 96 typically has an axial widthsufficient to ensure that the entire axial width of weld surfaces 88(FIG. 12) is heated by hot air blown out of exit openings 96 and 93.Weld heater 36 and its components are typically constructed of materialssuch as metal that can easily withstand high temperatures whileresisting deformation.

Compression mechanism 38 comprises a set of pinch rollers 100 and 102 tocompress the portions of sheet material 11 heated by heater 36 to weldthe back seam. Roller 100 is rotatably mounted on frame 2 via an axle110 to rotate about an axis X3 which extends axially and is horizontalin the sample embodiment. Roller 102 is rotatably mounted on frame 2about an axle 114 to rotate about an axis X4 which is parallel, adjacentand offset from axis X3. Axes X3 and X4 are typically parallel to axesX1 and X2. Roller 102 is a driven roller such that a drive mechanism isoperatively connected to and drives rotation of roller 102. Forinstance, rotation of roller 100 may be driven by a conventionalmechanical drive assembly 104 such as a chain and sprocket or belt andpulley. However, any suitable drive mechanism may be used.

Rollers 100, 102 are positioned closely adjacent and downstream ofdownstream end 94, exit opening 96, downstream edge 77 and 93 and exitopening 93. Each of rollers 100 and 102 has a cylindrical outer surface.Portions of each of these cylindrical surface bounds or definestherebetween a short portion 109 of pathway 9 which serves as acompression passage through which sheet material 11 passes and in whichmaterial 11 is compressed. In the sample embodiment, the top of thecylindrical outer surface of roller 100 and the bottom of thecylindrical outer surface of roller 102 are closely adjacent one anotherand define therebetween this short portion of pathway 9, and when nosheet material is between rollers 100 and 102, this top and bottom ofsaid cylindrical outer surfaces may be in contact with one another.These cylindrical outer surfaces may be formed of metal, a polymeric orplastic material, or any suitable material capable of withstanding theoperational temperatures created downstream of welding tip 99 of heater36. Compression mechanism 38 also includes a compression controller 117(FIGS. 2-3) which may include pneumatic or hydraulic actuatorspositioned and operatively connected to rollers 100 and 102 to press atleast one of rollers 100 and 102 toward the other of rollers 100 and102. Controller 117 controls the amount of force applied to achieve thispressing of one or both rollers. While rollers 100 and 102 are typicallyused to provide compression of sheet material 11, other knowncompression devices may be used, such as pinch belts. For example, a setof pinch belts is disclosed in U.S. Patent Application Publication No.2012/0227363.

With primary reference to FIGS. 4 and 5, weld breaker assembly 39 isdescribed. Assembly 39 includes leg or shaft 28 and a rigid flat plate101 which is L-shaped as viewed from above and typically horizontal.Thus, heat shield assembly 29 and weld breaker assembly 39 share acommon leg, shaft or rod 28. Plate 101 is typically formed of a piece ofsheet metal. L-shaped plate 101 is rigidly secured to and extendshorizontally downstream from shaft 28 in a cantilever fashion to a freeor terminal downstream end or edge of plate 101. Plate 101 may besecured to shaft 28 by a rigid mounting flange 103 which is rigidlysecured to and extends downstream from shaft 28 a short distance. Flange103 is shown as a flat horizontal plate which is vertically thicker thanplate 101. Plate 101 is rigidly secured to flange 103 and extendsdownstream therefrom in cantilever fashion.

Plate 101 includes a longitudinally elongated leg 120 and an axiallyelongated leg 122 and has a flat upwardly facing first or top surface124 and a parallel flat downwardly facing second or bottom surface 126which faces away from surface 124. Surfaces 124 and 126 may behorizontal. Leg 120 of plate 101 has two longitudinally elongatedopposed edges 128 and 130 and an upstream axially elongated edge 132from which edges 128 and 130 extend downstream horizontally andperpendicular to shaft 28 and edge 132 to an axially elongateddownstream end or edge 136 of longitudinal leg 120 and plate 101. Edge136 also serves as downstream end or edge of axial leg 122, which has anaxially elongated upstream end or edge 134. Edge 134 is substantiallyperpendicular to edges 128 and 130 and substantially parallel to shaft128. Edge 136 is shown as a shallowly curved edge which is generallyperpendicular to edges 128 and 130 and generally parallel to shaft 128and edge 134. Leg 122 has a free or terminal arcuate end edge 138 whichtransitions from the left end of edge 134 to the left end of edge 136.Edges 128-138 define the L-shape of plate 101. Surfaces 124 and 126 aretypically generally flat and substantially continuous between all edges128-130. Edges 128 and 130 are substantially parallel to the downstreamdirection (Arrows F) at the portion of pathway 9 in which edges 128 and130 are disposed. Edges 132, 134 and 136 are substantially perpendicularto the downstream direction at the portion of pathway 9 in which edges132, 134 and 136 are disposed.

Weld breaker 40 is a portion of axial leg 122 which is adjacent anddirectly downstream of compression passage 109 defined between pinchrollers 100 and 102. (Where pinch belts are used instead of pinchrollers, weld breaker 40 is adjacent and directly downstream of ananalogous compression passage defined between the pinch belts.) Weldbreaker 40 is adjacent and downstream of rollers 100 and 102 (or pinchbelts where used) of compression mechanism 38. Edge 134 of breaker 40 isstraight in the exemplary embodiment and serves as a breaker surface orbreaker edge for breaking incidental welds as discussed further below.L-shaped plate 101 is entirely within pathway 9, and thus each componentthereof, including legs 120 and 122 and weld breaker 40 are entirelywithin pathway 9. Leg 120 is adjacent and axially offset (here, to theright) or spaced from heat shield assembly 29 (plates 30, 32 and 84),passage 34, pinch rollers 100 and 102, compression passage 109 andwelding tip 99. Leg 122 extends to the left beyond the left sides ofpinch rollers 100 and 102 and passage 109 and extends to the rightbeyond the right sides of pinch rollers 100 and 102 and passage 109.

Downstream drive roller 21 is downstream of the weld breaker 40. Roller21 is axially elongated and extends outwardly beyond pathway 9 to theleft and right. Roller 21 has a cylindrical outer surface and may beconstructed of materials similar to the upstream drive roller 20.Upstream drive roller 20 is rotatably mounted such as by a bearing 49 tothe frame of welder 10. A drive mechanism 51 is operatively connected tothe roller 21. Drive mechanism 51 may be a motor configured to rotateroller 21 about an axis X5 which is parallel to axes X1-X4. Downstreamidle roller 23 is adjacent and directly above roller 21. The cylindricalouter surface of roller 23 may have a diameter smaller than roller 21.Roller 23 is rotatably mounted to the frame of welder 10 so as to berotatable about an axis X6 which is parallel to axes X1-X5. Thecylindrical outer surfaces of rollers 21 and 23 define therebetween apassage or portion of pathway 9.

The operation of welder 10 will be described after a brief descriptionof the formation of sheet material into a tubular configuration. Sheetmaterial 11 is typically unwound from a bulk sheet material roll 12(FIG. 1) upstream of components 14 and moves downstream therefromthrough a bag former or tuber of components 14 (FIG. 1). The bag formeror tuber of 14 forms sheet material 11 into a tubular configurationhaving a first or bottom panel 15 and a second or top panel 13. Panels13 and 15 are superimposed. Panel 13 includes a first segment 17 and asecond segment 19 which overlap one another in an unwelded overlapregion 140 which welder 10 subsequently forms into a welded back seam11A (FIGS. 7, 11, 12, 14) as sheet material 11 moves downstream withinpathway 9. As shown in FIG. 9, each of panels 13 and 15 has a width W1,left panel segment 17 has a width W2, right panel segment 19 has a widthW3, and overlap region 140 and back seam 11A have a width W4. Width W1is the normal axial distance from side edge 9C to side edge 9D. Width W2is the normal axial distance from side edge 9C to a terminallongitudinal edge 142 of panel segment 17. Width W3 is the normal axialdistance from side edge 9D to a terminal longitudinal edge 144 of panelsegment 19. Width W4 is the normal axial distance from edge 142 of panelsegment 17 to edge 144 of panel segment 19. The sheet material 11 whichis formed into the tubular configuration by tuber 14 may or may not havepleated edges or additional folds along the edges 9C and 9D. The formedmaterial leaves the bag former and flows downstream in its formed butunwelded state. Welder 10 forms the welded back seam 11A as sheetmaterial move downstream through pathway 9. Thereafter, welded sheetmaterial 11 with back seam 11A may move further downstream from welder10 to the downstream components 16 where additional functions areperformed to create additional seams such as a bottom seam and possiblya top seam.

The operation of welder 10 is shown with primary reference to FIGS.7-14. Reference herein to downstream movement of sheet material 11 as itpasses through welder 10 means downstream movement of sheet materialwithin pathway 9. The sheet material 11 in the tubular configurationcreated by the tuber 14 (FIG. 1) material moves into welder 10 at itsupstream end in sheet material pathway 9, passing through passage 56between rollers 20 and 22, as shown in FIGS. 7 and 8. Sheet material 11remains in this generally flat tubular configuration as it movesdownstream through welder 10, first without seam 11A upstream ofcompression mechanism 38 and subsequently with seam 11A downstream ofcompression mechanism 38. Controls of welder 10 control the rotation ofdrive rollers 20 and 21 to facilitate downstream movement of material 11at an appropriate flow rate. After sheet material passes through passage56, panel segments 17 and 19 are separated from one another byseparation shaft 24 adjacent and downstream of the rollers 20, 22. Shaft24 thus extends between segments 17 and 19 and separates overlappingweld surfaces 88 of segments 17 and 19 in the overlap region 140 whilesegments 17 and 19 slidably engage opposite sides of shaft 28 as sheetmaterial 11 continues moving downstream. One of segments 17 and 19 (here19) is directly above and closely adjacent or in contact with shaft 24and the other of segments 17 and 19 (here 17) is directly below andclosely adjacent or in contact with shaft 24. Shaft 24 creates a gap 58(FIG. 8) within pathway 9 between weld surfaces 88 of panel segments 17and 19. During downstream movement of sheet material 11, a portion ofsegment 24D is directly between panels 17 and 19 in overlap region 140,and a portion of segment 24D is directly between panels 19 and 15axially offset from overlap region 140 (and thus not directly betweenpanels 17 and 19).

Segments 17 and 19 and weld surfaces 88 continue to move downstream in abifurcated or spaced apart manner (by gap 58) towards and alongmanifolds 60 and 62 of preheater assembly 26. Each of manifolds 60 and62 is in gap 58. During downstream movement of sheet material 11, eachof manifolds 60 and 62 are directly between panels 17 and 19 in overlapregion 140 and directly between panels 15 and 19 in overlap region 140.As sheet material moves downstream along and past manifolds 60 and 62,panels 17 and 19 are closely adjacent or in contact with opposite sidesof each of the manifolds, and may slidably engage these opposite sidesor surfaces of the manifolds. Manifolds are heated in accordance withsuitable controls of welder 10 and in turn provide heat to heat weldsurfaces 88 of panels 17 and 19 as sheet material 11 moves downstreampast the manifolds. In the exemplary embodiment, the blower of thepreheater assembly blows or forces heated air through the manifoldinterior chambers and out of holes 66 directly onto surfaces 88 topreheat surfaces 88. The preheater simultaneous preheats both of weldsurfaces 88 as sheet material passes or moves downstream adjacentmanifolds 60 and 62. Although hot or heated air 87 (FIG. 10) may be usedto heat weld surfaces 88, other heaters may be used. Hot air 87 may beapproximately between 100° C. and 800° C. depending of the specificsheet material used and the downstream flow rate of the sheet material.(In one example, when the material flow stream is advancing at adownstream flow rate of approximately 120 M/min, the temperature of thehot air 87 flowing through the preheater assembly 26 may beapproximately between about 300° C. and about 400° C.) Generally, hotair 87 is usually within a range of about 100° F. to about 1450° F.Controls of welder 10 control the temperature setting as needed.

As shown in FIGS. 11 and 12, sheet material in the tubular configurationmoves downstream from preheater 26 around and past shaft 28 such thatthe heated and bifurcated weld surfaces 88 are closely adjacent or incontact with shaft 28, whereby surfaces 88 of panels 17 and 19 mayslidably engage opposite sides of shaft 28 during the downstreammovement, such as the top and bottom sides or surfaces 68, 70. Shaft 28keeps weld surfaces 88 separate prior to compression between the pinchrollers of compression mechanism 38. Immediately after moving past shaft28, sheet material 11 continues moving downstream past plates 30, 32 and84 and pinch roller 100 and 102 of compression mechanism 38. As sheetmaterial 11 moves downstream past plates 30, 32 and 84, the sheet edgeor portion of segment 19 in overlap region 140 (including weld surface88 of segment 19) passes through passage 81. Weld surface 88 of panelsegment 19 is closely adjacent or in contact with surface 72 of plate 30as panel segment 19 moves downstream past plate 30, whereby surface 88of panel segment 19 may slidably engage surface 72 during downstreammovement of sheet material 11. The surface of panel segment 19 whichfaces opposite weld surface 88 of panel 19 is closely adjacent or incontact with surface 79 of plate 84 as panel 19 moves downstream pastplates 30 and 84, whereby said opposite surface of panel 19 may slidablyengage surface 79 during downstream movement of sheet material 11. Weldsurface 88 of panel segment 17 is closely adjacent or in contact withsurface 76 of plate 32 as panel segment 17 moves downstream past plate32, whereby surface 88 of panel segment 17 may slidably engage surface76 during downstream movement of sheet material 11. Edge 144 is alsoclosely adjacent or in contact with surface bend or connecting wall 85segment 19 moves downstream past plates 30, 32, 84 and wall 85, wherebyedge 144 of segment 19 may slidably engage wall 85 during downstreammovement of sheet material 11.

As sheet material 11 moves downstream from shaft 28 toward passage 109between pinch rollers 100, 102, the portions of segments 17 and 19within overlap region 140, including weld surfaces 88, move closer toone another until surfaces 88 are forced into contact with one anotherby the force which forces or compresses at least one of rollers 100, 102toward the other of rollers 100, 102. These portions of segments 17 and19 thus taper toward one another along in a manner analogous to thetapering of plates 30 and 32 toward one another. As these portions ofsegments 17 and 19 are moving downstream along plates 30 and 32, weldheater 36 is heated within heater passage 34 to further heat weldsurfaces 88 to increase their temperature beyond that produced bypreheater assembly 26 to a welding temperature which allows them to bethermally welded to one another when compressed together by compressionmechanism 38. In the exemplary embodiment, as overlap region 140 movesdownstream beyond the tapered plates 30, 32, the blower of heater 36blows hot air 86 (FIG. 12) onto weld surfaces 88 to the desired weldingtemperature as region 140/surfaces 88 pass between roller 100 and 102 inpassage 109. More particularly, hot air 86 is blown through heater 36through inlet end 90 to outlet end 92 out of exit opening 96 of nozzle94 into the downstream portion of passage 34 and out of exit opening 93between segments 17 and 19 of overlap region 140 directly onto weldsurfaces 88 to heat surfaces 88 to the desired welding temperature. Exitopening 96 is adjacent the portions of weld surfaces 88 being heated byhot air 86, typically an inch or less upstream of said portions of theweld surfaces 88.

Weld heater 36 raises the temperature of weld surfaces 88 to allow thematerial 11 forming surfaces 88 to weld to one another upon passingthrough compression mechanism 38 and cooling sufficiently. Typically,heater 36 heats weld surfaces 88 to a welding temperature which meltssurfaces 88, which are then pressed together by rollers 100, 102 andcooled to form welded back seam 11A. Generally, the applied amount ofheat from weld heater 36 is in a range of about 100° F. to about 1450°F., although this may vary depending on the specific material 11 and theflow rate at which the material 11 is moving downstream. Controls ofwelder 10 control the temperature setting as needed.

Sheet material 11 continues moving downstream past the welding tip ofheater 36 and the downstream ends of plates 30 and 32 to pass betweenrollers 100 and 102. As material 11 moves downstream between roller 100and 102, roller 100 rotates (Arrow R3 in FIG. 12) about axis X3 androller 102 rotates (Arrow R4 in FIG. 12) about parallel axis X4 in adirection opposite that of roller 100. As sheet material movesdownstream between rollers 100, 102, cylindrical outer surface 108 ofroller 100 rollingly contacts the outer or bottom surface of bottompanel 15 directly below overlap region 140 while the cylindrical outersurface of roller 102 rollingly contacts the outer or top surface ofsegment 19 of top panel 13. Under the control of appropriate controls ofwelder 10, hydraulic, pneumatic or other actuators of compressionmechanism 38 are actuated to apply pressure of rollers 100 and 102toward one another. Rollers 100 and 102 thus press or force panels 13and 15 against one another in overlap region 140, specifically so thatsegments 17 and 19 in overlap region 140 are pressed or forced againstone another and so that segment 17 in overlap region 140 and the portionof panel 15 immediately adjacent region 140 are pressed or forcedagainst one another. Inasmuch as heater 36 applies heat to region 140immediately upstream of roller 100 and 102, sufficient heat may beapplied to segment 17 in region 140 and/or to panel 15 immediatelyadjacent region 140 to cause undesired incidental welds 146 (FIG. 12A)to form between segment 17 in region 140 and panel 15 immediatelyadjacent region 140. These incidental welds 146 thus may also be said toextend between back seam 11A and panel 15.

As shown in FIG. 12A, weld breaker 40 is positioned to break and therebyeliminate these undesired incidental welds 146, thereby leaving behindbroken welds 146A between back seam 11A and panel 15, or between segment17 in region 140 and panel 15 immediately adjacent/opposite region 140.More particularly, sheet material 11 continues moving downstream beyondthe pinch rollers of compression mechanism 38 so that back seam 11A andpanel 15 immediately adjacent seam 11A moves past weld breaker 40,thereby breaking any incidental welds 146 that had formed between seam11A and panel 15. In the exemplary embodiment, back seam 11A travelsdownstream directly over breaker 40 of axial leg 122 while the portionof panel 15 adjacent region 140 and seam 11A travels downstream directlyunder breaker 40. Breaker edge 134 breaks welds 146 as sheet material 11moves downstream relative to the stationary breaker 40, thus leavingseam 11A intact and eliminating welds 146 to leave behind broken welds146A. As material 11 moves downstream, the inner surface of seam 11A isclosely adjacent or in contact with top surface 124 of breaker 40 andmay thus slidably engage surface 124. Likewise, the inner surface ofpanel 15 is closely adjacent or in contact with bottom surface 126 ofbreaker 40 and may thus slidably engage surface 126 during downstreammovement of sheet material 11.

Broken welds 146A extend inwardly respectively from the inner surface ofseam 11A (or inner surface of panel 17 in region 140) and the innersurface of the portion of panel 15 in region 140. The broken welds 146Awhich extend inwardly (here downwardly) from the inner surface of seam11A (or inner surface of panel 17 in region 140) thus extend inwardlytoward the broken welds 146A which extend inwardly (here upwardly) fromthe inner surface of the portion of panel 15 in region 140. Broken welds146A are formed of or from sheet material 11 and are thus the samematerial as that making up panels 13 and 15 and any gusset panels wheregussets are included in forming the sheet material tube having seam 11A.More particularly, incident welds 146 are formed by melting andsubsequent solidification of material 11 of panel 17 in overlap region140, whereby the solidified material 11 of welds 146 when broken bybreaker 40 makes up welds 146A.

As sheet material is moving downstream and welds 146 are being broken,breaker 40 is also forcing the separation of seam 11A and the portion ofpanel 15 in region 140 from one another to form therebetween a space 150which is part of the interior chamber defined between panels 13 and 15of the newly seamed tube of sheet material 11. Space 150 is between theinner surface of seam 11A (or inner surface of panel 17 in region 140)and the inner surface of the portion of panel 15 in region 140. Space150 is thus also between the broken welds 146A which extend inwardly(here downwardly) from the inner surface of seam 11A (or inner surfaceof panel 17 in region 140) and the broken welds 146A which extendinwardly (here upwardly) from the inner surface of the portion of panel15 in region 140. During downstream movement of sheet material 11,breaker 40 is directly between the inner surface of seam 11A (or innersurface of panel 17 in region 140) and the inner surface of the portionof panel 15 in region 140.

During downstream movement of sheet material 11, breaker 40 is directlybetween the inner surface of seam 11A (or inner surface of panel 17 inregion 140) and the inner surface of the portion of panel 15 in region140; a portion of segment 28D, leg 120 and a portion of leg 122 (betweenleg 120 and breaker 140) is directly between panels 19 and 15 axiallyoffset from seam 11A or region 140 on one side of seam 11A or overlapregion 140 (and thus not directly between panels 17 and 19); a portionof leg 122 (including end edge 138) is directly between panels 17 and 15axially offset from seam 11A or overlap region 140 on the opposite sideof seam 11A or overlap region 140; a portion of segment 28D is directlybetween panels 17 and 19 in overlap region 140; a portion of plate 30and a portion of plate 32 inside pathway 9 are directly between panels17 and 19 in overlap region 140 and directly between panels 15 and 19 inoverlap region 140; a portion of plate 30 and a portion of plate 32inside pathway 9 are directly between panels 15 and 19 axially offsetfrom seam 11A/overlap region 140 (and thus not directly between panels17 and 19) because said portions of plate 30 and 32 extend axiallyoutwardly beyond edge 142 of panel 17 away from edge 144 of panel 19; aportion of plate 32 outside pathway 9 extends axially outwardly beyondedge 144 of panel 19 away from edge 142 of panel 17 so that said portionoverlaps a portion of panel 17 without overlapping any portion of panel19; plate 84 is outside pathway 9 overlapping (directly above) panels19, 17 and 15 in region 140; a portion of heater passage and welding tipor leg 99 including nozzle 94 and exit opening 96 are directly betweenpanels 17 and 19 in region 140 and directly between panels 15 and 19 inregion 140.

Once seam 11A is formed and incidental welds 146 are broken, sheetmaterial continues downstream past weld breaker 40, between rollers 21and 23, and may enter components 16 (FIG. 1) for further processing. Thetube of sheet material 11 having back seam 11A typically remains in asubstantially flat configuration as it moves downstream from rollers 21and 23 out of the downstream end of welder 10 and into the components16. Typically, components 16 include a bag bottomer which cuts thetubular sheet material 11 with back seam 11A into tubular pieces andforms a seam along one end of each tubular piece to form respectivebottom edges of bags which includes seam 11A, whereby the bags may befilled with bulk materials during additional downstream bag formationprocesses 16.

Because back seam 11A may be welded by the use of heat and compressiononly, back seam 11A may be free of adhesives, stitching, meltablematerials (e.g. hot melt glue) other than material 11 itself or anyother material which is distinct or different from material 11. Thus,welder 10 allows for the rapid production of bags without the need foradditional processes such stitching or the application of adhesives orhot melt glues etc. to produce the back seam.

In the foregoing description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued.

Moreover, the description and illustration of the preferred embodimentof the invention are an example and the invention is not limited to theexact details shown or described.

The invention claimed is:
 1. A thermal welding apparatus comprising: asheet material pathway adapted to allow sheet material to movedownstream therethrough in a direction substantially parallel to alongitudinal axis of the pathway; a weld heater extending adjacent thepathway; a compression mechanism extending adjacent the pathway adjacentand downstream of the weld heater; and a weld breaker assembly whichcomprises a first axial leg upstream of the compression mechanism, asecond axial leg downstream of the compression mechanism, and alongitudinal leg extending from the first axial leg to the second axialleg; wherein the longitudinal leg and the second axial leg together forman L-shaped member when viewed from above, wherein the L-shaped memberis rigidly secured to and cantilevers from the first axial leg, andterminates in a free terminal end located downstream of the compressionmechanism; wherein the second axial leg serves as a weld breaker whichis within the pathway and adapted to disengage incidental welds createdduring formation of a longitudinally-oriented welded back seam of thesheet material as the sheet material is moving downstream through thepathway.
 2. The apparatus of claim 1 wherein the weld breaker is a pieceof sheet metal.
 3. The apparatus of claim 1 wherein the weld breaker ispart of a flat plate.
 4. The apparatus of claim 1 further comprising alip and a plate adjacent the weld heater which define therebetween asheet edge receiving space adapted to receive therein an edge of thesheet material.
 5. The apparatus of claim 1 wherein the first axial legcomprises a first portion outside the pathway and a second portion inthe pathway; the second axial leg is entirely within the pathway; andthe longitudinal leg is entirely within the pathway.
 6. The apparatus ofclaim 1 wherein the longitudinal leg is a plate.
 7. The apparatus ofclaim 1 wherein the first axial leg is a cantilevered rod.
 8. Theapparatus of claim 7 wherein the second axial leg and the longitudinalleg are configured as a plate.
 9. The apparatus of claim 8 wherein thelongitudinal leg is axially offset from the compression mechanism. 10.The apparatus of claim 9 wherein the compression mechanism comprises apair of pinch rollers; and the longitudinal leg is axially offset fromthe pinch rollers.
 11. The apparatus of claim 1 further comprising apreheater assembly extending within the sheet material pathway upstreamof the weld heater.
 12. The apparatus of claim 11 further comprising aseparation shaft extending into the sheet material pathway adjacent andupstream of the preheater assembly.
 13. The apparatus of claim 12further comprising first and second rollers adjacent and upstream of theseparation shaft; wherein the rollers define therebetween a portion ofthe pathway.
 14. The apparatus of claim 1 wherein the compressionmechanism comprises a pair of pinch rollers defining therebetween aportion of the pathway.
 15. The apparatus of claim 1 further comprisinga heater shield assembly which defines a heater passage within thepathway; and a portion of the weld heater in the heater passage.
 16. Theapparatus of claim 15 wherein the heater shield assembly comprises firstand second shield plates which extend within the pathway and definetherebetween the heater passage.
 17. The apparatus of claim 16 whereinthe shield plates taper towards each other from upstream to downstream.18. The apparatus of claim 16 wherein the heater shield assemblycomprises a lip adjacent the first shield plate so that the lip andfirst shield plate define therebetween a sheet edge receiving spaceadapted to receive therein an edge of the sheet material.
 19. Acombination comprising: flexible thermoplastic sheet material in atubular configuration comprising first and second superimposed panels,wherein the second panel includes a longitudinally-oriented overlapregion comprising a first edge segment of the first panel and a secondedge segment of the second panel, wherein the second edge segmentoverlaps the first edge segment; a thermal welding apparatus throughwhich the sheet material is movable downstream; a weld heater of thethermal welding apparatus extending adjacent the overlap region; acompression mechanism of the thermal welding apparatus which is adjacentand downstream of the weld heater and which compresses the first andsecond edge segments and the first panel; a longitudinally-orientedwelded back seam formed between the first and second edge segmentsdownstream of the compression mechanism; incidental welds formed betweenthe welded back seam and the first panel; and a weld breaker assemblywhich comprises a first axial leg upstream of the compression mechanismand a second axial leg downstream of the compression mechanism, and alongitudinal leg extending from the first axial leg to the second axialleg; wherein the longitudinal leg and the second axial leg together forman L-shaped member when viewed from above, wherein the L-shaped memberis rigidly secured to and cantilevers from the first axial leg, andterminates in a free terminal end located downstream of the compressionmechanism; wherein the first axial leg extends between the first andsecond edge segments, the second axial leg extends between the weldedback seam and the first panel, and the second axial leg serves as a weldbreaker which disengages the incidental welds as the sheet materialmoves downstream.